This invention relates generally to well casings, and more particularly to insulated well casings.
In considering the environment to which an oil well casing would be exposed in the Prudhoe Bay area of Alaska, certain new requirements were developed. In this vicinity there exists a layer of permafrost; i.e., a layer of subsurface soil which may extend down 2,000 feet and is permanently frozen. If a well is drilled utilizing the same approach followed in temperate climates the oil (which is approximately 180.degree. F.) passing through the well casing will cause the permafrost about the well casing to melt. The melting of the permafrost causes it to subside, exerting downward drag on the well casing which may cause failure. Moreover, if the flow of oil is terminated, the soil surrounding the casing will eventually refreeze which may produce forces sufficient to cause the casing to collapse.
Even in temperate climates a fluid may become excessively viscous as it flows to the surface if its natural heat is not retained sufficiently.